An offscreen GLDrawable using BITMAP on Windows shall expose the same behavior than other impl. Culprit is WindowsBitmapWGLDrawable, which flips the GDI DiB via BITMAPINFOHEADER's height field while assigning the negative height. This shall not be done, since we don't read out the DiB directly, but via OpenGL.
Depends on Bug 720, since cleaning up GLContextImpl* is required to move property 'GLContext.isGLOrientationFlippedVertical()' to 'GLDrawable.isGLOriented()' where it belongs! Windows BITMAP GLDrawable impl. isGLOriented() shall return false, while we keep the BITMAPINFOHEADER's height field negative to remove the need for vertical flip when used w/ AWT or Windows, .. Then property 'GLDrawable.isGLOriented()' has to be recognized throughout the utility functions, i.e. TextureData's mustFlipVertically and hence TextureIO writer.